1. Field of the Invention
The present invention relates to a file sharing system and a method of using the file sharing system to generate a single logical directory structure.
2. Description of the Related Art
In order to share data between a plurality of computers that are distributed on a network, a file-sharing device known as NAS (Network Attached Storage) is used. Data are produced on a daily basis while the client terminals that utilize the data also increase. Hence, data of a large volume must be managed by using a plurality of NAS.
However, when accessing a desired file, a user must specify a physical NAS in which the file is stored and must access the NAS. In other words, even when the user knows the file name, unless the user knows the physical storage location of the file, it is not possible to access the file.
Therefore, only when a certain file is moved from a first NAS to a second NAS is it necessary to notify each user of the movement of the file. In addition, in cases where the NAS is added in order to improve the performance, an obsolete NAS is switched for a new NAS and the number of client terminals increases, for example, which is time-consuming for the system administrator. Therefore, in recent years, a system that generates a single logical directory structure by virtualizing the directory structures of the respective NAS has been proposed (Japanese Application Laid Open No. 2007-35030, Japanese Application Laid Open No. 2003-58408, U.S. Patent Application Number 2006/0010169).
In the prior art, the directory structures of a plurality of NAS are virtualized as a single logical directory structure and supplied to a client terminal. Hence, even when a physical NAS increase or reduction or the like occurs, this does not affect the logical directory structure. As a result, the user is able, by using the logical directory name used thus far, to access the desired file without consideration of the change to the physical constitution.
However, such patents are lacking with respect to disaster recovery. In a system where disaster recovery is considered, data are synchronized at a plurality of sites and, even when a first site stops due to a fault, access to a file at the second site is possible. Such patents do not disclose a system constitution that considers disaster recovery and, therefore, there is a margin for improvement with respect to fault tolerance.